mrpruthvinandan.
In a terminal such as Konsole or any other command line interface ( cli ) for short at the $ prompt type: su : hit enter then type in your root password & hit enter.
In the graphical environment right click on blank space on desktop, click run command & type : kdesu dolphin :
replace dolphin with the application you wish to run as root but exercise extreme caution here.

if you is asking how to login as root in the graphical mode, beggining from the login screen, this is not possible to make from KDE, only from GNOME, but....
you will not becomes a root user, but a system root....!
is VERY DANGEROUS to your system this procedure!